(1) Field of the Invention
The present invention relates to a novel nitrile hydratase and the DNA encoding the nitrile hydratase, from a thermophilic Bacillus sp., which is constitutively expressed, activated in the presence of cobalt ions, active within a temperature range of 5.degree. C. to 70.degree. C. and a pH range of 5 to 9, and stable at elevated temperatures of 50.degree. C. to 60.degree. C. in the presence of acrylonitrile for a significant period of time. Further, the present invention relates to the use of the nitrile hydratase to produce acrylamide which is used for forming polymers.
(2) Description of Related Art
Enzymatic formation of acrylamide from acrylonitrile offers advantages over the traditional copper-catalyzed process in reduction of unwanted waste products and decreased energy input, making the process a promising example of utilization of enzymes for development of "green" processes for commodity chemical production (Ashina, Y., et al., in Industrial Applications of Immobilized Biocatalysts, A. Tanaka, T. Tosa, T. Kobayashi, eds. Marcell Dekker, N.Y. p. 91-107 (1993)). Nitrile hydratases capable of catalyzing this hydration have been found in a wide variety of bacteria (Yamada, H., et al., Biosci. Biotech. Biochem. 60:1391-1400 (1996); and Cramp, R., et al., Microbiology 143:2313-2320 (1997)). Nitto Chemical Company, Japan, has pioneered the utilization of the nitrile hydratase from Rhodococcus rhodochrous J1 for the production of acrylamide from acrylonitrile. The R. rhodochrous nitrile hydratase is a novel enzyme which contains cobalt bound at the active site. The cobalt ion containing nitrile hydratases provide more attractive catalytic features than ferric ion-containing nitrile hydratases (Nagasawa, T., et al., Appl. Microbiol. Biotechnol. 40:189-195 (1993)). Although the Nitto acrylamide process is in successful production, their bioconversion process uses immobilized non-viable whole cells in the process which is run at a temperature below 10.degree. C. and with modest acrylonitrile concentrations in order to prevent inactivation of the hydratase enzyme catalyst by the acrylonitrile substrate and to avoid product polymerization (Nagasawa, T., et al., Appl. Microbiol. Biotechnol. 40:189-195 (1993)).
U.S. Pat. No. 4,001,081 to Commeyras et al describes the use of various mesophilic bacterial species from the genus Bacteridium (in the sense of Prevot), genus Micrococcus (in the sense of Bergey), genus Bacillus and genus Brevibacterium (in the sense of Bergey) for conversion of nitriles to amides. In particular, the strain R 332, a mesophilic Bacillus species, was cited as having nitrilasic activity. R332 was shown to have optimal growth between 20.degree. C. and 40.degree. C. (see U.S. Pat. No. 5,563,053 to Takashima et al). In the nitrilasic reaction with any of the above bacteria, the pH is maintained at the pH value which is limiting for the hydrolysis of the amide to its acid. The reaction temperature is 25.degree. C.
U.S. Pat. No. 4,248,968 to Watanabe et al describes a process to convert acrylonitrile to acrylamide by using bacteria strains from either Corynebacterium or Nocardia genera. However, bacteria from genus Bacillus, genus Bacteridium, and genus Brevibacterium were also recited as being useful. The nitrile hydratase described has high activity but has low heat resistance and is inactivated in a rather short time period at temperatures between 25.degree. C. and 30.degree. C. Therefore, while the reactions are performed between 0.degree. and 30.degree. C., the reactions are preferably performed at 15.degree. C. or less.
U.S. Pat. No. 4,629,700 to Prevatt et al relates to conversion of aromatic polynitriles having no hydroxyl groups to an aromatic compound having at least one cyano group and one amide group or acid group. The invention discloses Rhodococcus species which have nitrilase systems capable of selectively hydrolyzing various cyano groups of the polynitrile. The nitrilase systems are induced either prior to or simultaneously with conversion of the aromatic polynitrile. The conversion of a dinitrile to a nitrile amide according to the invention is performed within the temperature range of 15.degree. to 35.degree. C.
U.S. Pat. No. 4,637,982 to Yamada et al relates to a process which uses various Pseudomonas species to cause the conversion of a nitrile to its corresponding amide. The process is performed under alkaline conditions at a temperature between the range of 0.degree. to 20.degree. C. The cells prior to use in the process are cultivated in the presence of an inducer (e.g., isobutyronitrile in the case when acrylonitrile is to be hydrated).
U.S. Pat. No. 5,130,235 to Beppu et al describes isolated DNA of Rhodococcus sp. N-774 encoding nitrile hydratase activity and recombinant E. coli containing the DNA. The nitrile hydratase activity appears to require Fe.sup.+ ions. A method for producing the nitrile hydratase in culture medium is also disclosed.
U.S. Pat. No. 5,135,858 to Yamada et al describes a Rhodococcus rhodochrous strain J-1. wherein a lactam induces the nitrilase activity in the cultured strain which is then used for the conversion of a nitrile to its corresponding acid. The conversion process is performed under temperatures ranging from 5.degree. to 50.degree. C. and within a pH between 4 and 10.
U.S. Pat. No. 5,334,519 to Yamada et al describes the use of cobalt cores with Rhodococcus rhodochrous strain J-1 to enhance the action of the nitrile hydratase in the conversion of a nitrile to its corresponding amide. In particular, the bacteria is cultivated in culture medium containing cobalt ions and a nitrile or amide inducer to induce the nitrile hydratase. The bacteria is then used for the conversion process which is performed at a temperature between 15.degree. to 50.degree. C. and a pH that is usually between 7 to 9.
U.S. Pat. No. 5,563,053 to Takashima et al describes a process for production of amide compounds from their nitrile precursor using the thermophilic bacterium Bacillus smithii strain SC-J05-1. The nitrile hydratase activity is inducible when a nitrile compound or an amide compound is added to the culture medium. The useful temperature range for the conversion process is between 0.degree. and 70.degree. C.
The foregoing provide attractive methods for production of an amide from its corresponding nitrile, in particular acrylamide from acrylonitrile. However, utilization of many of these nitrile hydratase enzymes has been limited by the requirement that very low temperatures be used for the bioconversion conditions, which increases production costs by requiring the reactions to be cooled.